In the field of surgery, it is well known to utilize vacuum aspiration for the removal of bodily fluids and irrigating fluids at the surgical site. In addition, in recent years vacuum aspiration has been used in conjunction with mechanical surgical cutters to enhance the effectiveness of the mechanical devices by drawing soft tissue into the mechanical cutting jaws by means of vacuum induction.
For example, in ophthalmological surgery, there have been developed devices for cutting and removing the fibrous vitreous material found within the eyeball. Such devices commonly employ a pair of concentric needles, the outer needle having an intake port adjacent to the distal end thereof. The inner needle is adapted to reciprocate within the outer needle, and includes a sharpened tip which reciprocates past the intake port of the outer needle. In such a device, tissue is drawn into the cutting port by means of vacuum aspiration applied through the needle assembly, the inner cutting tip shearing the tissue drawn into the port. The sheared tissue is then aspirated through the inner needle and delivered to a collection bottle.
Generally speaking, the aspirating vacuum applied to the port of the surgical instrument is created by a vacuum source which is applied to the collection bottle. Thus the vacuum applied to the collection bottle is delivered from that bottle through a flexible tubing connection to the surgical instrument.
A significant characteristic of such surgical instruments known in the prior art is that the rate at which tissue is excised and aspirated is primarily dependent upon the level of vacuum applied at the intake port of the instrument. If the vacuum level is too low, the tissue removal will proceed too slowly. However, if the vacuum level is too high, tissue will be drawn into the cutting instrument too rapidly. In this latter instance, tissue which should not be cut may be drawn into the instrument inadvertently, causing great damage to the eye. Thus it is clear that precise control of the level of vacuum applied to the mechanical cutter must be maintained at all times by the surgeon.
Generally speaking, such prior art surgical devices include a vacuum collection bottle which is sufficiently large to receive the maximum volume of effluvia (tissue, irrigation fluid, blood, etc.). Thus the collection bottle has a substantial volume which must be evacuated to the desired level to effect proper cutting of the surgical tool. However, the desired vacuum level changes from moment to moment in a surgical proceedure, in accordance with the nature of the tissue being cut, the proximity of the cutter to delicate tissues which must not be damaged, and the like. Moreover, whenever the surgical cutting tool is halted, even momentarily, the vacuum level within the collection bottle generally reverts to atmospheric pressure.
Due to the large volume of the vacuum collection bottle, a small but significant time period is required to reestablish the vacuum level within the collection bottle, or to alter the vacuum level to a new, desirable level. This time period, which may range from two to three and one-half seconds, requires the surgeon to proceed extremely slowly to avoid critical surgical errors. For example, when the surgeon is increasing the vacuum level to cut and remove denser or more fibrous tissue, the lag in response time of the vacuum aspiration system may cause the surgeon to believe that the new higher vacuum level is insufficient, when in fact the higher level has not yet been reached. The surgeon will then switch to an even higher vacuum level, in order to effect cutting of the heavier tissue. When these incremental increases in the vacuum level are finally delivered to the cutting port of the instrument, after a lag time of a few seconds, the vacuum level may be much too great and the resulting inrush of tissue into the cutting port may cause damage to surrounding tissues.